18th annual conference on manual control.pdf - Acgsc.org

The focus of the present study was to determine what aspects
of different task situations cause an individual's experience
of workload and related factors to vary. Subjective rating
scales provide one method of evaluating workload (Bird, 1981;
Hicks & Wierwille, 1979; Jex & Clement, 1979_ Williges &
Wierwille, 1979), partlcularly when combined and compared with
objective performance measures. The present study built on previous
research (Bird, 1981) which examined the effect of different
factors on the the individual's experience of workload
using a single-axis compensatory tracking task with six levels
of difficulty. Subjects rated each level of the tracking task
using a 15 bipolar-adjective scale that addressed a variety of
factors assumed to be related to the subjective experience of
workload. Factors related to the difficulty levels of the ta_k
were: skill required, task difficulty, controllability, and
task demands. The increase in subject effort (stick input} was
shown to be related to evaluations of skill required, task complexity,
task difficulty, and'task demands.
In the present experiment four different tasks (including
several levels of the tracking task used by Bird), each with
four levels of difficulty, were presented to the subjects, who
were required to rate each level of each task immediately after
its performance using a modified version of the earlier scale.
Although the tasks chosen for use in this experiment (compensatory
tracking, the Sternberg task, auditory monitoring, and time
estimation} are commonly employed as secondary measures of workload,
in this instance they were used only as primary tasks in
order to obtain ratings that would stand alone and thus be useful
for future research comparisons where these tasks will function
as secondary tasks.
Subjects
METHOD
Twelve general aviation pilots, ten males and two females,
21 to 43 years old, served as paid volunteers. All subjects
were right handed.
Apparatus
All experimental sessions were conducted in a small,
sound-attenuated experimental chamber. The subject was seated
in a comfortable chair approximately 100 cm away from the
Cathode Ray Tube (CRT) screen. The control stick used for the
tracking task was located on the right arm of the chair. The
button press used for the time estimation task was centrally
mounted on the top of the control stick. Press buttons used for
both the Sternberg memory task and the auditory monitoring task
were mounted on the left arm of the chair, with all functions
clearly labeled. The analog control for rating evaluations was
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